Lepr Rev (2007) 78, 110– 121
Impaired warm and cold perception thresholds
in leprosy skin lesions
MANOEL F. VILLARROEL*,**, MARIA BEATRIZ
P. ORSINI*,***, MARIA APARECIDA F. GROSSI*
& CARLOS MAURICIO F. ANTUNES*
*Programa de Pós-Graduação em Ciências da Saúde: Infectologia e
Medicina Tropical, Faculdade de Medicina, Universidade Federal de
Minas Gerais (UFMG), Belo Horizonte, MG, Brazil
**Departamento de Neurofisiologia Clinica do Hospital Ortopédico,
Belo Horizonte, MG, Brazil
***Unidade Básica de Saúde de Citrolândia, Betim, Minas Gerais,
Brazil
Accepted for publication 14 February 2007
Summary The aim of the present study was to determine the frequency of alteration
in warm perception thresholds (WPT), cold perception thresholds (CPT) and the
warm and cold perception interval (WCPI) in leprosy-suspected skin lesions, and to
determine if these tests could assist in the diagnosis of leprosy. Tests were conducted
using a thermal sensory analyser TSA-2001 (Medoc Ltd, Israel) and the method of
levels. A cross-sectional study of 112 patients presenting leprosy-suspected skin
lesions (‘patch’), with no clinical evidence of peripheral nerve damage, was
conducted. Leprosy diagnosis was based on clinical dermato-neurological
examinations and complementary tests. One hundred and eight subjects (45 males,
63 females; average age 37·7 years) completed the tests: 82 were positively diagnosed
with leprosy and 26 with diseases of different etiologies. The mean values of WPT
(45·63 ^ 5·59), CPT (9·64 ^ 11·34) and WCPI 36·01 ^ 15·58) registered in leprosyskin lesions were significantly different (P , 0·001) from lesions of diverse
aetiologies and skin area without lesions. The cut-off point for WPT as determined
from the ROC curve (receiver operating characteristic) was 35·108C, with a
sensitivity of 90·2% and a specificity of 100%, and the corresponding cut-off point for
CPT was 28·958C, with a sensitivity of 92·7% and a specificity of 100%.
Nevertheless, all patients with leprosy presented a WCPI greater than 6·108C (ROC
curve) in skin lesions. Increase in the thermal thresholds indicated warm
hypoaesthesia, cold hypoaesthesia or both. The WCPI, which embraces both warm
and cold perception thresholds, was the best indicator of thermal sensation, a term
used in literature as a non-specific expression that does not describe warm and cold
stimuli explicitly in terms of units of temperature.
Correspondence to: M. F. Villarroel, Rua Ten. Brito Melo, 1365 – sala 601, 30180-070, Belo Horizonte, MG,
Brazil (Tel: þ 55 31 32926534; Fax: þ55 31 32926534; e-mail: [email protected])
0305-7518//064053+12 $1.00
q Lepra
110
Thermal perception in leprosy skin lesions
111
Introduction
Hansen’s disease or leprosy is a chronic infectious disease caused by Mycobacterium leprae,
which affects the peripheral nervous system, skin, and other tissues.1 – 5
The cardinal signs of the disease are cutaneous lesions with altered sensation,
enlargement of the peripheral nerve and slit skin smears show in alcohol-acid resistant fast
bacilli.1 – 4 The skin lesions, and lesions of the peripheral nerves may be associated, but they
may appear separately.6 – 10 The initial cutaneous manifestations of leprosy result from direct
infection of the dermal nerves, and are characterised by hypochromic lesions or erythema
with reduced sensation.1 – 4,11 Verification of altered tactile, thermal or pain sensation of
suspected skin lesions (‘patch’) confirms a diagnosis of leprosy.1 – 4,12 In early lesions,
temperature or pain sensation may be impaired, while touch sensation is preserved.12,13
However, in more advanced stages of the disease, all forms of sensation are impaired.12
In Brazil,14,15 sensation in leprosy (skin lesions and areas supplied by major nerve trunks)
is commonly tested using Semmes –Weinstein monofilaments (SWM) to measure lightpressure thresholds, as well as standard clinical sensory tests employing cotton wool,
pinpricks, and tubes containing hot (458C) and cold (48C) water in order to evaluate,
respectively, tactile, pain and thermal sensation. The SWM kit consists of monofilaments
standardised to deliver forces of 0·05 g (green), 0·2 g (blue), 2 g (purple), 4 g (red), 10 g
(orange) and 300 g (magenta). Normal reference value is 0·05 g in any region of the body,
except for the soles of the feet (2·0 g). The standard clinical sensory tests, however, make
comparisons difficult between examinations carried out at different stages of the disease,
because of the difficulties in controlling the many variables intrinsic to these tests.16 Several
instruments have been developed to evaluate thermal sensation in leprosy-suspected lesions,
for example, the Temperature Sensation Testing and Grading device,17,18 the Thermosense
device,19,20 and the Thermal Stability Tester.12 However, according to Zaslansky and
Yarnitsky,21 while altered temperature and vibration thresholds may be used as indicators of
the sensory losses characteristic of leprosy, non-uniform and unconventional testing
techniques render evaluation of the results obtained somewhat difficult. In 1976, Fruhstorfer
and collaborators22 developed the Marstock stimulator, which employs heat and cold stimuli
to evaluate routinely the small myelinated A-delta fibres and the unmyelinated C fibres.
Measurement of the warm perception threshold (WPT) and the cold perception threshold
(CPT), through application of heat and cold stimuli, not only allows quantification of loss of
the thermo-sensitive function in the form of hypoesthesia and hypoalgesia, but also of the
hyperfunction in the form of thermal hyperalgesia.21 – 24 While these tests are not specific for
evaluating the peripheral nervous system in leprosy, they are useful for the evaluation of
small fibres and their cutaneous receptors in the study of focal and generalised peripheral
neuropathies of any aetiology.21,23,25 Thermal thresholds were determined for cool and warm
sensation, and for heat perceived as pain,26 in leprosy skin lesions, but the detailed results
were not presented. In 2005, Van Brakel et al. reported on thermal sensation in the skin areas
supplied by major nerve trunks.27,28
The aim of the present study was to determine the frequency of alteration in WPT, CPT
and the warm and cold perception interval (WCPI) in leprosy-suspected skin lesions, and to
determine if these tests could assist in the diagnosis of leprosy. Patients with signs and
symptoms involving major nerve trunks have not been included in this study.
112
M. F. Villarroel et al.
Patients and methods
PATIENTS
A cross-sectional study involving 112 patients from various leprosy health centres located in
the metropolitan area of Belo Horizonte (MG, Brazil) was performed during the period from
January 2000 to November 2004. The project was undertaken following approval by the
Ethical Committee of UFMG, and an appropriate form containing the Terms of Consent was
signed by each of the participants. Patients older than 7 years and with leprosy-suspected skin
lesions with diameters . 18 mm (i.e. presenting thermal stimulation areas of at least
16 £ 16 mm) were included in the study. Potential subjects with neurological alterations and
those with clinical histories of alcoholism, diabetes mellitus and other metabolic or genetic
disorders, which could result in the impairment of the central and peripheral nervous system,
were excluded.
For each patient, tactile sensation towards cotton wool, thermal sensation towards warm
and cold water tubes, pain sensation towards pinpricks, and SWM values (at 0·05, 0·2, 2·0,
4·0, 10·0 and 300·0 g) of leprosy-suspected lesions and contralateral (opposite side of the
body) and ipsilateral (same side of the body) skin area without lesion (SAWL) were
determined. The areas investigated were circumscribed with a pen, and patients were
redirected to the Clinical Neurophysiology Laboratory of the Orthopaedic Hospital (Belo
Horizonte) for investigation of the thermal thresholds of the lesions. In patients with multiple
lesions, one lesion with an appropriate area for application of the thermal stimulus and
subsequent biopsy was selected. The results of the investigations carried out at the health
centres were not available to the hospital laboratory technicians in order to guarantee the
blind nature of the study. Following thermal studies of the areas previously selected, patients
returned to their original health centres to receive a definitive diagnosis and specific
treatment. Data collected at the health centres and at the hospital were correlated only after a
definitive diagnosis of leprosy had been achieved.
LEPROSY DIAGNOSIS
The diagnosis of leprosy was based on clinical dermo – neurological examination together
with complementary examinations including skin biopsy and histopathology, slit-skin
smears, evaluation of SWM, standard clinical sensory tests (cotton, pinpricks and tubes
containing hot and cold water), Mitsuda reaction, anti PGL-1 serology (ML flow), and
histamine and pilocarpine tests. For some patients, a further period of observation was
required before a definitive diagnosis could be reached.
CONTROLS
Subjects either with or without leprosy diagnosis have been used in the control group. The
controls consisted of contralateral and ipsilateral SAWL of patients who had been diagnosed
with leprosy, and of skin lesions and contralateral and ipsilateral SAWL of patients in whom
leprosy was excluded.
Thermal perception in leprosy skin lesions
113
EQUIPMENT AND PROCEDURES
The temperature of the room in which the thermal tests were conducted varied between 23·0
and 26·28C, and patients were allowed no visual contact with the equipment throughout the
test period. Tests were conducted using a thermal sensory analyser TSA-2001 (Medoc Ltd.,
Israel) with a thermode of stimulation area 16 £ 16 mm. The adaptation temperature (AT) of
the thermode was 328C and the temperature limits were fixed at 50 and 08C for warm and cold
perception, respectively. The rate of change of temperature during the application of a
stimulus was 18C/s, while the rate of change during the return to the base line was 0·88C/s.
The interval between the application of each was 4 – 6 s. Temperatures below and above the
AT (for the determination of CPT and WPT, respectively) were recorded continuously
between the set limits with an accuracy of 0·18C. For patients who did not perceive the
extreme temperatures, values of 50 or 08C were registered, as appropriate, in order to permit
statistical analysis.
A standard test sequence, involving the determination of CPT and WPT of the
contralateral SAWL, then of the suspected lesion, and finally of the ipsilateral SAWL was
applied to each subject. The thermode was placed carefully over the selected test area and
fixed with adhesive tape in order to ensure good contact with the skin in the absence of
excessive pressure. The skin around the area to be stimulated was surrounded with thermal
insulating tape. The method of levels29 was used to determine perception thresholds in which
a series of stimuli of fixed intensities was applied to the subject (Figure 1). After an initial
temperature step of 48C and the return to AT, subjects were questioned about their perception
of the stimulus. A positive response led to a smaller subsequent stimulus, whilst a negative
response was matched with a larger subsequent step. The step size was halved when the
response of the subject changed from positive to negative, and vice versa. The step size
remained unaltered when the response of the subject remained unchanged. The sequence of
stimuli was continued until a step size of 0·18C was attained.
STATISTICAL ANALYSIS
The mean values of the parameters measured for leprosy and control groups were compared
using Student’s t-test (when the variables presented a normal distribution) and nonparametric tests (Mann –Whitney and Wilcoxon) for asymmetric distributions. Wilcoxon and
paired t-tests were used to compare data obtained for suspected lesions and contralateral
Figure 1. Schematic diagram of the method of levels employed to determine WPT showing the intensity of heat
stimulus applied to the test area following a positive (Y, yes) or a negative (N, no) response by a subject concerning
their perception of the previous stimulus. AT is the adaptation temperature of the thermode and dashed line is the
sensory threshold finally determined.
114
M. F. Villarroel et al.
SAWL, suspected lesions and ipsilateral SAWL, and contralateral SAWL and ipsilateral
SAWL. To evaluate and validate the performance of the thermal test for the diagnosis of
leprosy, a receiver operating characteristic (ROC) curve was used, which shows a graphic
representation of the sensitivity and specificity of the test and allows the selection of a more
appropriate cut-off point as determined by the definitive diagnosis. The statistical software
used for the analysis of the data was SPSSw 11·5 (SPSS Inc, Chicago, IL, USA) values were
deemed statistically significant at P , 0·05.
Results
One hundred and 12 patients presenting with leprosy-suspected skin lesions were redirected
to the Clinical Neurophysiology Laboratory, from which 108 (45 males and 63 females)
concluded all of the tests. Three patients abandoned the tests, and one patient did not
understand the procedures involved in the thermal tests and could not complete the
examination. The age of patients with leprosy-suspected lesions ranged from 9 to 73 years
with an average age of 37·7 ^ 14·9 years. The average age of patients with leprosy was
37·4 ^ 13·2, and 93·5% of this group were younger than 60 years old. The average age of
patients without leprosy was 38·7 ^ 18·7 years. The evolution of leprosy had occurred within
30 days to 60 months, and 72·2% of patients reported that leprosy-suspected lesions
developed in less than 12 months. Leprosy was diagnosed in 82 patients (75·9%) and the
characteristics of the lesions were of indeterminate type (13·4%), tuberculoid type (28%),
borderline tuberculoid type (51·2%) and borderline borderline type (7·3%). Leprosy lesions
predominated in the lower limbs (36·6%), followed by the upper limbs (31·7%), trunk
(24·4%) and face (7·3%). Twenty-six patients were diagnosed with vitiligo, pityriasis alba,
granuloma annulare, atopic dermatitis, pseudo-lymphoma, post-inflammatory residual
dischromia and fungal mycosis. The number of suspected skin lesions in each patient varied
between one and eight: 37 patients presented with only one lesion, of whom 22 were
diagnosed with other diseases.
WARM AND COLD PERCEPTION THRESHOLDS
The mean values of WPT (45·638C) and CPT (9·648C) of lesions of the leprosy group were
significantly different (P , 0·001) from the corresponding mean values obtained from lesions
of diverse etiologies (Table 1). In the group in which leprosy had not been diagnosed, there
were no statistically significant differences between the corresponding mean values of WPT
and CPT of skin lesions and contralateral SAWL, of suspected lesions and ipsilateral SAWL,
and of contralateral SAWL and ipsilateral SAWL. Similarly, in the leprosy group there were
no significant differences between the respective mean values of WPT and CPT of
contralateral and ipsilateral SAWL.
Within the leprosy group, the mean value of the absolute differences between WPT of
skin lesions and contralateral SAWL was 12·418C, while the mean value of the absolute
difference between the corresponding CPT was 21·328C (Table 2). These values were similar
to the absolute differences between the corresponding WPT and CPT (12·36 and 21·318C,
respectively) of leprosy lesions and ipsilateral SAWL. However, in the control group,
there were no statistically significant differences between the mean values of the
absolute differences between WPT or CPT of non-leprosy lesions and contralateral SAWL,
Table 1. Mean values of warm perception threshold (WPT), cold perception threshold (CPT) and warm and cold perception interval (WPCI) obtained for suspected lesions,
and contralateral and ipsilateral skin areas without leprosy (SAWL) in the group diagnosed with leprosy (leprosy) and without leprosy (non-leprosy)
WPT
CPT
Mean ^ standard deviation (8C)
WCPI
Mean ^ standard deviation (8C)
Mean ^ standard deviation (8C)
Non-leprosy
Leprosy
P-value
Non-leprosy
Leprosy
P-value
Non-leprosy
Leprosy
P-value
Suspected lesion
Contralateral SAWL
Ipsilateral SAWL
33·28 ^ 0·70
33·27 ^ 0·60
33·28 ^ 0·67
45·63 ^ 5·59
33·23 ^ 0·81
33·27 ^ 0·78
, 0·001
0·819
0·929
30·84 ^ 0·88
30·77 ^ 0·83
30·75 ^ 0·79
9·64 ^ 11·34
30·96 ^ 0·57
30·95 ^ 0·58
, 0·001
0·272
0·236
2·43 ^ 1·11
2·49 ^ 1·12
2·54 ^ 1·09
36·01 ^ 15·58
2·27 ^ 1·16
2·31 ^ 1·17
, 0·001
0·389
0·364
Thermal perception in leprosy skin lesions
Tested skin area
115
116
M. F. Villarroel et al.
Table 2. Mean values and ranges of the absolute differences in warm perception threshold (WPT), cold perception
threshold (CPT) and warm and cold perception interval (WCPI) between suspected lesions, contralateral and
ipsilateral skin area without leprosy (SAWL) in the group diagnosed with leprosy (leprosy) and without leprosy
(non-leprosy)
Mean ^ standard deviation (8C)
(range: minimum – maximum)
Parameters
Differences in WPT
Suspected lesion and
contralateral SAWL
Suspected lesion and ipsilateral
SAWL
Contralateral and ipsilateral
SAWL
Differences in CPT
Suspected lesion and
contralateral SAWL
Suspected lesion and ipsilateral
SAWL
Contralateral and ipsilateral
SAWL
Differences in WCPI
Suspected lesion and
contralateral SAWL
Suspected lesion and ipsilateral
SAWL
Contralateral and ipsilateral
SAWL
Non leprosy
Leprosy
P-value
0·30 ^ 0·23 (0·0–0·7)
12·41 ^ 5·68 (0·2 –17·6)
,0·001
0·30 ^ 0·29 (0·0–1·00)
12·36 ^ 5·68 (0·1 –17·5)
,0·001
0·20 ^ 0·16 (0·0–0·5)
0·17 ^ 0·17 (0·0 –1·2)
0·28 ^ 0·33 (0·1–1·4)
21·32 ^ 11·33 (0·1–31·6)
,0·001
0·28 ^ 0·34 (0·0–1·3)
21·31 ^ 11·34 (0·0–31·6)
,0·001
0·18 ^ 0·24 (0·0–1·1)
0·14 ^ 0·13 (0·0 –0·9)
0·33 ^ 0·31 (0·0–1·3)
33·74 ^ 15·68 (4·6–49·0)
,0·001
0·36 ^ 0·39 (0·0–1·8)
33·70 ^ 15·68 (4·6–49·1)
,0·001
0·28 ^ 0·31 (0·0–1·6)
0·23 ^ 0·20 (0·0 –1·3)
0·355
0·264
0·391
non-leprosy lesions and ipsilateral SAWL, and of contralateral and ipsilateral SAWL of all
patients. The mean values of the absolute differences of WPT and of CPT between leprosy
lesions and contralateral SAWL, and leprosy lesions and ipsilateral SAWL, were significantly
different (P , 0·001) from the corresponding values of the control group. The cut-off point
for WPT as determined from the ROC curve was 35·108C, with a sensitivity of 90·2% and a
specificity of 100%, and the corresponding cut-off point for CPT was 28·958C, with a
sensitivity of 92·7% and a specificity of 100% (Table 3).
Table 3. Cut-off point, sensitivity and specificity of warm perception threshold (WPT), cold perception threshold
(CTP), warm and cold perception interval (WCPI), and the absolute difference of temperature of warm and cold
perception interval (Dt WCPI) obtained from the receiver operating characteristic (ROC) curve
Parameters
WPT
CPT
WCPI
Dt WCPI
Cut-off point (8C)
ROC curve
Sensitivity (%)
Specificity (%)
35·10
28·95
6·10
2·95
90·2
92·7
100
100
100
100
100
100
Thermal perception in leprosy skin lesions
117
WARM AND COLD PERCEPTION INTERVAL
Within the leprosy group, the mean value of WCPI of lesions was 36·018C, while the
corresponding values of contralateral SAWL and of ipsilateral SAWL were 2·27 and 2·318C,
respectively (Table 1). In the group in which leprosy had not been diagnosed, the mean values
of WCPI of skin lesions, contralateral SAWL and ipsilateral SAWL were 2·43, 2·49 and
2·548C, respectively. Patients with leprosy presented a WCPI superior than 6·108C (the cutoff point determined from the ROC curve). As shown in Table 2, within the group presenting
leprosy-diagnosed lesions, the mean value of the absolute differences between the WCPI of
lesions and contralateral SAWL (33·748C) was very similar to the mean value of the
differences between the WCPI of lesions and ipsilateral SAWL (33·708C). However, the
mean values of the absolute differences of WCPI of skin lesions and contralateral SAWL, and
of skin lesions and ipsilateral SAWL, between the leprosy group and the non-leprosy group
were significantly different (P , 0·001). Patients with leprosy had presented absolute
differences of WCPI between skin lesions and SAWL (contralateral and ipsilateral) equal or
superior to 4·608C (the cut-off point was 2·958C).
Discussion
It is well recognised that some cutaneous and pure neural forms of leprosy are very
difficult to diagnose. In spite of the acknowledged importance of thermal sensation
measurements in the diagnosis of cutaneous forms of leprosy, evaluations of these
modalities continues to be conducted using non-quantitative approaches including the
warm and cold water tube techniques. The quantitative sensory thermotest may be affected
by various factors 22,23,25,29 – 37 that reduce their reproducibility. Such factors include the
equipment and methodology employed, the size of the stimulated area, the initial
temperature of the stimulator, the rate of change of temperature, and the region of the
body tested. Following the introduction of the Marstock stimulator, a number of different
types of instruments have become commercially available.38 However, the results obtained
using the recently-introduced technology must be compared with the thermal thresholds
already established, and for this purpose it is necessary to apply the same equipment,
methodology and algorithms.39
In the present study, the methodology employed afforded values of WPT, CPT and WCPI
of the leprosy skin lesions (Table 1) that were significantly higher than those of lesions
of different aetiologies (P , 0·001). The observed increase in WPT indicated a warm
hypoaesthesia occasioned by the involvement of the C fibres and their specific receptors, while
the increase in CPT indicated a cold hypoesthesia with the involvement of A-delta fibres or
their specific receptors. Pure warm hypoaesthesia is common in neuropathy. Although the
study was carried out with patients with skin lesions, with no signs or symptoms of peripheral
neuropathy (trunks), we expected to register a higher WPT alteration in relation to CPT.
However, on the basis of the cut-off points adopted (cf. Table 3), the sensitivities and
specificities of the WPT and CPT values were similar, indicating that both parameters have
the same practical importance in the diagnosis of leprosy. The observed increase in WCPI
indicated the functional involvement of either C fibres, or A-delta fibres, or both.
Leprosy lesions can be located in diverse regions of the body and different regions of the
body of healthy individuals exhibit significantly different thermal thresholds.22,24,25,39
Nevertheless, it is not practical to establish a standard reference for the diagnosis of leprosy
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M. F. Villarroel et al.
for each one of the body areas. As shown above, however, suspected lesions, contralateral
SAWL and ipsilateral SAWL in the control group had similar mean values of WPT, CPT and
WCPI (Table 1). These results confirmed those of previous studies in which no significant
differences could be established in thermal thresholds when comparing contralateral
symmetric cutaneous areas,39 or neighbouring skin areas in the same segment of the body.37
A difference of more than 18C in thermal threshold (WPT or CPT) between a suspected area
and a symmetric normal area is considered as clinically valuable.40 In the present study, one
patient in the control group presented absolute difference of this magnitude in CPT,
comparing lesion (fungal mycosis) and contralateral SAWL. Another four patients presented
differences of more 18C in WPT or CPT, comparing lesions of different etiologies and
ipsilateral SAWL and comparing contralateral and ipsilateral SAWL. Such differences,
however, did not alter statistically the mean values of the groups in which the patients were
included. In the leprosy group the absolute differences in WPT or CPT between lesions vs
contralateral SAWL and lesions vs ipsilateral SAWL were less than 18C in 13 (15·8%)
patients.
For individuals of the leprosy group, the minimum absolute difference between the WCPI
of lesions and the WCPI of contralateral or ipsilateral SAWL was found to be 4·608C (cut-off
point at 2·958C). Such a temperature difference is 2·5 times larger than the greatest difference
(1·88C) recorded in the control group (Table 2). Thus, in order to ensure a more reliable
comparison of thermal thresholds it is important to evaluate contralateral areas or
neighbouring areas in the same segment.
None of the subjects in the present study exhibited normal thresholds for warm and cold
stimulus simultaneously. The WCPI value, which embraces both WPT and CPT parameters,
was the best indicator of thermal sensation, a term used in the literature as a non-specific
expression that does not describe warm and cold stimuli explicitly in terms of units of
temperature. Through a comparative study of the absolute differences in the values of WCPI
temperatures (i.e. for lesions vs contralateral SAWL and lesions vs. ipsilateral SAWL, Tables
2 and 3) considering a cut-off point of 2·958C or establishing a cut-off point of 6·108C for
WCPI of the lesion (Table 3), it was possible to establish a cut-off point for thermal sensation
in a suspected lesion predictive of a definitive diagnosis of leprosy. The advantage in
employing the absolute difference of WCPI (since SAWL had been used as control of the
patient) is that it not only permits the simultaneous evaluation of warm and cold stimuli, but it
also reduces the importance of various factors that interfere with the determination of thermal
thresholds, such as the inclusion or not of the reaction time, the size of the thermode, the rate
of temperature change, the region of the body tested, and the age of the individual.
Some studies31,36,41 have indicated that the thermal threshold of the feet of healthy
individuals increases as a function of age, particularly in subjects older than 65 years. In the
present study, only four patients were 65 years or more, but their age did not significantly
affect the mean values of the thermal threshold of the group in which they were included.
The large standard deviations obtained for WPT, CPT and WCPI in leprosy-diagnosed
patients (as shown in Tables 1 and 2) indicate that the lesions investigated were of a
heterogeneous nature, involving not only several clinical forms of the disease, but lesions of
different evolution times (30 days to 60 months), many of which may not have been
accurately reported by the patients themselves. The thermal sensations across the spectrum of
leprosy lesions are presented in Table 4.
Thermal receptors are very sensitive to differences between the temperature of the skin
and the objects that are touched. Warmth and cold receptors are more sensitive to changes in
Thermal perception in leprosy skin lesions
119
Table 4. Mean values in warm perception threshold (WPT), cold perception threshold (CPT) and warm and cold
perception interval (WCPT), in different forms of leprosy
Mean ^ SD (8C)
Leprosy
Indeterminate
Tuberculoid
Borderline tuberculoid
Borderline borderline
Patients
WPT
CPT
WCPT
11
23
42
6
45·1 ^ 4·7
45·9 ^ 5·8
46·0 ^ 5·7
43·1 ^ 5·8
15·4 ^ 8·7
6·8 ^ 10·3
9·2 ^ 11·7
13·4 ^ 14·9
29·6 ^ 12·6
39·1 ^ 14·3
36·9 ^ 16·4
29·7 ^ 18·1
skin temperature than constant temperatures.42 The temperature range was truncated at 0 and
508C. Other devices allow the use of temperature higher than 508C. However, warmth
receptors fire most vigorously at skin temperature of 458C. If the stimulus temperature
exceeds 458C, warmth fibres fire an intense burst of impulses and then cease firing even if the
heat stimulus is maintained. Stimuli above 508C fail to excite warmth fibres.42 Cold receptors
fire most vigorously at skin temperature of 258C and the nociceptive threshold is around
58C.42
A clear temporal distinction between the moment of warm or cold perception and the pain
caused by these stimuli have been noticed when the WPT was lower than 468C and the CPT
was higher than 68C. Nevertheless, stimuli above 468C or below 68C have been, respectively,
referred to as heating or cooling perception of fast installation immediately followed by pain
(Villarroel et al., in preparation). Twenty-two leprosy patients (26·8%) did not report warm
sensation or heat pain in the skin lesions at 508C while thirty patients (36·5%) did not refer to
cold sensation or cold pain at 08C. Three patients (indeterminate, borderline tuberculoid and
borderline borderline) reported in the lesions, paradoxical warm sensation during the
measurement of cold perception thresholds (Villarroel et al., in preparation).
The diagnosis of leprosy based on clinical dermo-neurological examination and
complementary tests was positive in 70 (85·3%) patients. SWM, cotton wool (tactile
sensation) and pinpricks (pain) tests have been applied to all patients. Nevertheless, thermal
tests (warm/cold water tubes) have been applied to 76 patients with leprosy (n ¼ 82) and, in
seven patients, the precise water temperature has not been reported.
Electronic thermal testing allowed the quantification of the thermal impairment in a
skin lesion. The patients evaluated were referred from health centers that work with
leprosy, and many of these patients were pre-selected by dermatogists in other works. It
would be important to include more subjects with early multibacilary disease and those
with skin lesions of different etiologies. Nonetheless, in a clinical and dermatological
examination we think that electronic thermal tests may, in addition, select patients for skin
biopsy.
The determination of warm and cold perception is simple, but it requires a certain level of
understanding, cooperation and concentration from the patient. The method of levels is rapid
to execute and does not depend on the reaction time of the individuals, hence the variability of
perception thresholds determined is minimised. The tests were easily applied and only one
patient could not complete the procedures. However, the application of this methodology is
limited by the cost and size of the equipment, and the large surface area of lesion required for
the application of the stimulus. Simpler and cheaper devices that permit the quantification of
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M. F. Villarroel et al.
temperature variation, and that consider values less than 508C and greater than 08C,
respectively, may be very useful in the field. The use of a smaller thermode is not only
important for the study of smaller lesions but also for the evaluation of potential thermal
mosaic effects in larger lesions. Patients presenting necrobiosis lipoidia, in which thermal
sensation may be altered,43 was not evaluated in the present study nor were comparisons
WPT, CPT and WCPI with other diagnostic methods.
In conclusion, it has been established that cutaneous lesions in leprosy-diagnosed patients
are characterized by alterations in thermosensation, functionally expressed as warm
hypoaesthesia, or cold hypoaesthesia, or both, through the determination of WPT, CPT and
WCPI values using the method of levels. Such tests are important mainly in refining the
diagnosis of pancibacillary leprosy.
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